In a variety of industries, such as the health care industry but also in other industrial applications, it can be necessary to monitor the effectiveness of processes used to sterilize equipment such as medical devices, instruments and other non-disposable articles. In these settings, sterilization is generally defined as the process of completely destroying all viable microorganisms including structures such as viruses and spores. As a standard practice, hospitals include a sterility indicator with a batch of articles to assay the lethality of the sterilization process. Both biological and chemical sterility indicators have been used.
One standard type of biological sterility indicator includes a known quantity of test microorganisms, for example Geobacillus stearothermophilus (formerly Bacillus stearothermophilus) or Bacillus atrophaeus (formerly Bacillus subtilis) spores, which are many times more resistant to a sterilization process than most contaminating organisms. After the indicator is exposed to the sterilization process, the spores can be incubated in a nutrient medium to determine whether any of the spores survived the sterilization process, with spore growth indicating that the sterilization process was insufficient to destroy all of the microorganisms. Although advances have been made, the time period for determining this with certainty can be undesirably long.
Available chemical sterility indicators can be read immediately at the end of the sterilization process. However, the results indicate only that a particular condition was present during the sterilization process, such as the presence of a particular chemical or a temperature for a certain period of time.
It is generally considered that the response of living organisms to all conditions actually present is a more direct and reliable test for how effective a sterilization process is in achieving sterilization. Accordingly, there is a continuing need for biological sterility indicators, which can indicate the effectiveness of a sterilization process without an excessive delay after completion of the sterilization process, and yet can provide a high level of confidence that various sterility parameters were reached in the sterilization process.